It has been described in U.S. Pat. Nos. 3,244,549 and 3,244,550, and British Pat. No. 1,135,540, etc. that various phenol compound are used as electron accepting compounds for pressure-sensitive recording materials or heat-sensitive recording materials. However, these phenol compounds are not always satisfactory. Namely, their color density is insufficient when used in combination with an electron donating colorless dye, and the fastness to light and moisture of the colored material after coloration is not sufficient.
With respect to sulfone compounds known hitherto, bisphenol S causes substantial fogging on the background (coloration of the part where printing was not carried out) or substantial fogging due to moisture, because it has considerable water-solubility. Further, hydroxydiphenyl sulfone compounds disclosed in European Patent Publication No. 67793 are not satisfactory electron accepting compounds, because they cause substantial fog due to their water solubility and provide images of low color density.